The present invention relates to apparatus for installation in an opening in a building wall or roof for the purpose of enhancing interior illumination by reflected sunlight, and to methods of determining the optimum orientation of reflectors to achieve maximum depth of penetration of reflected light into the area to be illuminated with acceptably low glare. In general terms, the invention relates to improvements in the technology commonly known as "beam daylighting."
Since the invention of the light bulb ana common availability of electrical power, most buildings have been designed under the assumption that electricity will supply interior illumination by way of lighting fixtures, and that it is unnecessary to rely upon natural light for most or all illumination purposes. Over the more recent past, this assumption has been challenged on several grounds. First, artificial lighting doesn't meet the needs of most visual tasks as well as does the broader spectral distribution of natural sunlight. Also, the luminous efficacy of natural light (around 113 lumens/watt) is substantially higher than that of all commonly-used luminaries (over twice that of fluorescents and eight times incandescents). In consequence, using natural light to meet illumination needs in buildings not only supplants electricity that would otherwise be used to power artificial light fixtures, but also lowers air conditioning loads. Thus, given good daylighting designs, the use of natural light is highly advantageous for a number of reasons.
As used herein, and generally in the field of interest, the term "beam daylighting" denotes the use of one or more light-reflecting surfaces which redirect the path of sunlight entering an enclosed area for visual or other illumination purposes. Among the prior art beam daylighting designs are those exemplified by U.S. Pat. Nos. 4,509,825, 4,630,8920, 4,634,222, 4,699,467 and 4,989,952. Some of the previously devised systems employ stationary reflectors, while others include means for moving the reflecting surfaces to track solar position. Planar, parabolic, and other configurations of reflecting surfaces have been used in beam daylighting applications, as have systems involving reflection of incoming light from two or more surfaces in distributing the light at the desired location. In any case, the reflecting surfaces have a longitudinal axis which, in all known prior art systems, is oriented either horizontally or vertically. As will be shown, optimum performance can be achieved only when the longitudinal axis of a single reflecting surface is oriented somewhere between horizontal and vertical. This is true whether the reflectors are fixedly installed, with their orientation providing optimized performance averaged over the period between successive solstices, or are movable to maintain optimized performance over a range of varying solar positions.
While it is generally recognized that orientation of the reflecting surface(s) should provide adequate lighting in all portions of the area to be illuminated (hereafter referred to for convenience as the room), prior art daylighting systems fail to adequately consider both the spatial and the temporal aspects of reflector orientation. That is, reflector performance must take into consideration both the distance of light penetration into the room and the level of glare in the area illuminated. Other design features, such as the relative cost, suitability for incorporation into existing structures, aesthetic appearance of the installed system, maintenance requirements, etc., are also often severely compromised or ignored.
Objects of the present invention are:
to provide a novel and improved beam daylighting system which fully or partially replaces artificial light with natural light at an acceptably low glare level;
to provide a method of determining optimal orientation of reflecting surfaces at a given site location to maximize distance of penetration of reflected light into a room (e.g., up to 30 feet) while eliminating or minimizing glare;
to provide beam daylighting structure wherein stationary reflecting surfaces are oriented to optimize room illumination at a given latitude when positioned in a wall or roof opening facing in a predetermined compass direction;
to provide a daylighting system which is easy to maintain, suitable for installation in both new and existing buildings, and compatible with a variety of residential, commercial, institutional and industrial environments;
to provide a highly effective daylighting system which, in a first embodiment, has no moving parts, is completely passive and functions without user interaction; and
to provide a daylighting system which, in a second embodiment, includes novel structural and operational components which reorient the reflector surfaces during periods when they receive direct sunlight to optimize the effectiveness of the system in terms of sending the reflected light in a desired direction.
Other objects will in part be obvious and will in part appear hereinafter.